The deployment of a spinning solar sail

Hibbert, Luke Thirkell (2019-04)

Thesis (MEng)--Stellenbosch University, 2019.


ENGLISH ABSTRACT: In recent years, interest in solar sailing has grown greatly, and significant research and resources are being contributed to its development and the development of similar and supporting technologies. Sailcraft utilise large deployable membrane structures to exchange momentum with photons in order to generate thrust from Solar Radiation Pressure. Many small solar sailing satellites make use of three-axis stabilisation and semi-rigid booms, however this design places limits on the sizes of sails possible due to the physical properties of these booms and the size of the deployment mechanisms required. Larger sails are desired in order to achieve greater solar thrust. The use of a spinning solar sailcraft with flexible booms makes it possible to deploy significantly larger sails, as the centrifugal force acts to deploy the sail and maintain the deployment thereof, eliminating the limits enforced by available semi-rigid boom technologies. The low cost and small size of CubeSats may be used to further develop spinning solar sail technology. This thesis focuses on the deployment of a spinning solar sail on a CubeSat platform. The dynamic equations which describe the behaviour of a spinning solar sailing satellite with flexible booms during- and post- deployment are developed. These equations, which describe the system, are used to investigate the behavioural trends in the deployment under various deployment strategies. Particular focus is given to the passive deployment of the sail booms. No direct active control is placed on the boom deployment in this case; the deployment rate is instead indirectly controlled through the spin rate of the satellite. This is achieved by the application of rotational damping to the pulley on which the booms are stowed and where from they are deployed. Passive deployment cases are investigated where control is based on strategies including free spin, centrifugal force-based control and constant spin rate control. The dynamics of active deployment, where the deployment rate is directly controlled, are also investigated. An experimental deployment mechanism is designed in order to validate the trends seen in the cases of passive deployment. This experimental deployment mechanism makes use of a geared rotary damper to apply a torque to the pulley from which the booms deploy - this slows the deployment rate with no external inputs. The trends seen in simulation are confirmed where possible. A control algorithm is developed, which is capable of detecting the deployment state of the booms based on the control input supplied to the motor driving the mechanism spin. Based on the deployment state detected, the spin rate of the mechanism can be appropriately adjusted. Based on the practical experience and insights gained from experimentation, the designs of three deployment mechanisms are presented. Two of the mechanisms designed make use of rotary dampers in different configurations in order to achieve passive deployment. The third mechanism is intended for actively controlled deployment and possess an actuator to control the deployment rate directly. The design takes advantage of centrifugal force, which allows the actuating motor and the mechanism as a whole to be very small in size.

AFRIKAANSE OPSOMMING: In die afgelope jare het belangstelling in sonseilvaart gegroei, en beduidende navorsing en hulpbronne word bygedra tot die ontwikkeling daarvan, en die ontwikkeling van soortgelyke en ondersteunende tegnologieë. Sonseil ruimtetuie gebruik groot ontplooibare membraanstrukture om momentum met fotone te ruil, ten einde om stoot van sonstralingdruk te genereer. Die meeste klein sonseil ruimtetuie maak gebruik van drie-as stabilisasie en halfstyf maste, maar hierdie ontwerp beperk die mate van seile moontlik as gevolg van die fisiese eienskappe van hierdie maste en die grootte van die vereiste ontplooiingsmeganismes. Groter seile word verlang om groter sonkrag te verkry. Die gebruik van ’n draaiende sonseil ruimtetuig met buigsame draad-en-massa maste maak dit moontlik om aansienlik groter seile te gebruik, aangesien die sentrifugale krag optree om die seil te ontplooi en die ontplooiing daarvan in stand te hou. Die grense word afgedwing deur beskikbare halfstyf mas tegnologieë. Die lae koste en klein grootte van CubeSats kan gebruik word om sonseilvaart tegnologie verder te ontwikkel. Hierdie proefskrif fokus op die ontplooiing van ’n draaiende sonseil op ’n CubeSat-perron. Die dinamiese vergelykings wat die gedrag van ’n draaiende sonseil ruimtetuig met buigsame maste, tydens en na die ontplooiing, beskryf word ontwikkel. Hierdie vergelykings, wat die stelsel beskryf, word gebruik om die gedragstendense onder verskillende ontplooiings strategieë te ondersoek. Daar word veral gefokus op die passiewe ontplooiing van die seil stelsel. Geen direkte aktiewe beheer word in hierdie geval geplaas op die ontplooiing van die maste nie. Die ontplooiingskoers word in plaas daarvan indirek beheer deur die draaitempo van die satelliet. Ontplooiing word bereik deur roterende demping aan die katrol toe te pas waarop die maste gestoor word en waar van hulle ontplooi word. Passiewe ontplooiingsgevalle word ondersoek waar beheer gebaseer is op strategieë insluitende van: vrye draai, sentrifugale kraggebaseerde beheer en konstante draaitempo beheer. Die dinamika van aktiewe ontplooiing, waar die ontplooiings spoed direk beheer word, word ook ondersoek. ’n Eksperimentele ontplooiingsmeganisme is ontwerp om die tendense wat in die gevalle van passiewe ontplooiing gesien word, te valideer. Hierdie eksperimentele ontplooiingsmeganisme maak gebruik van ’n roterende demper om ’n wringkrag aan die katrol toe te pas waaruit die maste ontplooi - dit vertraag die ontplooiingskoers sonder eksterne insette. Die tendense wat in simulasie gesien word, word waar moontlik bevestig. ’n Kontroleringsalgoritme word ontwikkel, wat die ontplooiingstoestand van die maste kan opspoor, gebaseer op die kontroleinset wat aan die motor wat die meganisme draaitempo aandryf, verskaf. Gebaseer op die ontplooiingstoestande wat opgespoor is, kan die draaitempo van die meganisme aangepas word. Op grond van die praktiese ervaring en insigte verkry uit eksperimentering, word die ontwerpe van drie ontplooiingsmeganismes aangebied. Twee van die ontwerpte meganismes maak gebruik van roterende dempers in verskillende konfigurasies om passiewe ontplooiing te bereik. Die derde meganisme is bedoel vir aktief beheer implementering deur ’n aktuator om die ontplooiingsvlak direk te beheer. Die ontwerp maak gebruik van sentrifugale krag, waardeur die aanstuurmotor en die meganisme as ’n geheel baie klein kan wees.

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